1. Field of the Invention
The present invention relates to an electron gun for a cathode ray tube display (CRT), and in particular, to an electron gun for a CRT that enhances the focusing characteristics by improving the image spreading of red, green and blue colors.
2. Description of Related Art
Generally, a CRT includes an electron gun for emitting electron beams, a deflection yoke for deflecting the electron beams, a shadow mask for color-selecting the electron beams, and a panel having a phosphor layer on an inner side. The electron beams emitted from the electron gun are deflected by the deflection magnetic field of the deflection yoke, and the deflected electron beams pass through the color-selecting shadow mask, followed by colliding with green, blue and red phosphors of the phosphor layer to emit light to display the desired images.
The electron gun for a CRT includes a cathode for emitting thermal electrons, a heater installed at the cathode to heat the cathode and emit thermal electrons, and a plurality of electrodes for focusing and accelerating the thermal electrons emitted from the cathode. The electrodes include first and second electrodes forming a triode portion together with the cathode, a plurality of focusing electrodes having focusing voltages applied thereto, and an anode electrode receiving a high anode voltage. The cathode, the first electrode, the second electrode, the focusing electrodes and the anode electrode are partitioned into three domains corresponding to the red, green and blue phosphors.
With the in line electron gun where the three domains are linearly arranged, the white balance image spreading occurs to a large extent due to the arrangement structure thereof, and the left and right difference occurs to a significantly extent with the electron beams placed at the left and the right sides corresponding to the red and the blue colors. For instance, for the electron beams corresponding to the red color, a relatively small beam is formed at the left side of the screen, and a relatively large beam is formed at the right screen side. Furthermore, for the electron beams corresponding to the blue color, a relatively large beam is formed at the left screen side, and a relatively small beam is formed at the right screen side. Accordingly, in the case of a white state where all the electron gun portions corresponding to the red, green and blue colors are operated, the peripheral beam focusing is deteriorated compared to that with one electron gun portion.
With the widening of the deflection angle to slim the CRT (the maximum deflection angle reaching up to 110° or more), the electron beams corresponding to the red color at the center of the screen represent the left sided image spreading, and the electron beams corresponding to the blue color represent the right sided image spreading, thereby differing from the CRT with the maximum deflection angle of 102-106°.
The electron beams corresponding to the red color at the first quadrant (the right upper side) of the screen represent the right sided image spreading, and the electron beams corresponding to the blue color represent the left sided image spreading. That is, in the case of a CRT having a widened deflection angle, the image spreading of the electron beams at the center and at the periphery of the screen is directed opposite to that of earlier CRTs. What is therefore needed is a new design for an electron gun that is better suited for the newer svelte, flat panel wide screen high deflection angle CRTs where less image spreading is produced and a higher quality image is produced.